Official (promoter-issued) 2nd printing 13&7/8 x 20&1/8" concert poster for the Grateful Dead appearing with Quicksilver Messenger Service at the Avalon Ballroom in San Francisco, CA on 1/27-28/1967.
Art by Stanley Mouse and Alton Kelley, image is # 45 in the Family Dog/Avalon series.
Medium flat index stock poster is in spectacular mint/near mint to near mint (A/A- to A-) condition; an absolutely GORGEOUS example of this classic Mouse/Kelley Grateful Dead image.
A quick check on the archive revealed a (disputed) tape of the show from the 27th; judge for yourself HERE: